An image forming apparatus hitherto known as an image forming apparatus for forming a multicolor image on a transferred member, such as a recording sheet or a transfer belt, is configured to uniformly electrify the surface of an image-carrying body, such as a photosensitive body, at a high voltage of predetermined polarity; to form an electrostatic latent image on the surface of the image-carrying body by means of exposing the surface of the electrified image carrier to the exposure unit; to form a toner image (the electrostatic latent image) by means of causing toner (a developing agent) of a predetermined color to adhere to the electrostatic latent image; and to transfer the toner image to a member to be transferred by use of transfer unit.
For example, a so-called tandem-type image forming apparatus having image-carrying bodies provided separately for individual colors is available as such an image forming apparatus which forms a multicolor image (see, e.g., JP-A-2001-166556).
The image forming apparatus of this type has a problem of occurrence of reverse transfer. Specifically, during the course of toner of a plurality of colors, which are charged with the same polarity (e.g., positive polarity) as that of a charged surface of an image-carrying body, being transferred to a transferred member through multi-transfer operation, a portion of the transferred toner is again reversely electrified (negatively electrified) and transferred back to the image-carrying body. When reverse transfer has arisen, the color balance of an image formed on the transferred member is lost, and there may arise a case where an image of a color, which is not intended by the user, is eventually formed.